“The coral die-off has caused radical changes in the mix of coral species on hundreds of individual reefs, where mature and diverse reef communities are being transformed into more degraded systems, with just a few tough species remaining,” explained Professor Andrew Baird, from the Centre of Excellence for Coral Reef Studies (Coral CoE) at James Cook University, co-author of the new report.

Coral bleaching, put simply, happens when environmental stress impacts on the “symbiotic” relationship between the rock-like living creatures that form the reefs and microscopic algae that give them their incredible colours.

When stressful factors, particularly the warming up of ocean waters because of climate change, take effect, the corals expel the algae, leaving them to become transparent skeletons.

Without the algae, the coral then starves.

Following on the 2016 heatwave impacts, the Great Barrier Reef suffered severe heat stress and bleaching last year.

Authors of the new study warn full recovery to pre-bleaching coral assemblages is unlikely to occur because coral colonies are continuing to die slowly and it takes at least a decade for even fast-growing species to replace them.

Yet Prof Terry Hughes, Director of the Coral CoE at James Cook University, has a sanguine approach to the successive losses. “That still leaves a billion or so corals alive, and on average, they are tougher than the ones that died,” he says.

“We need to focus urgently on protecting the glass that’s still half full, by helping these survivors to recover.

NC

The coral is NOT doomed if greenhouse emissions are quickly curbed

“The Great Barrier Reef is certainly threatened by climate change, but it is not doomed if we deal very quickly with greenhouse gas emissions.

Findings from the study, say scientists, highlights the need for assessing the risk of a widespread collapse of coral reef ecosystems, particularly if action on climate change fails to limit warming to below 1.5-2C pre-industrial averages.

Failure will radically alter reefs and undermine the benefits the provide to millions of people around the world, say the scientists.